Evaluation of revolving algae biofilm reactors for nutrients and metals removal from sludge thickening supernatant in a municipal wastewater treatment facility.

This work is to evaluate pilot-scale Revolving Algal Biofilm (RAB) reactors of two heights (0.9-m and 1.8-m tall) to treat supernatant from sludge sedimentation at Metropolitan Water Reclamation District of Greater Chicago (MWRD) for removing nutrients (N and P) as well as various metals. The RAB reactors demonstrated a superior performance in N and P removal as compared to control raceway ponds. Taller 1.8-m RAB reactors performed better than 0.9-m RAB reactors in terms of total nutrient removal and algal biomass productivity. At 7-day HRT, total P (TP) and Total Kjeldahl N (TKN) removal efficiency reached to 80% and 87%, respectively, while ortho-P and ammonia removal efficiency reached to 100%. Decreasing HRT led to an enhanced TP and TKN removal rate and nutrient removal capacity. At HRT of 1.3-day, the TP removal per footprint of 1.8-m tall RAB reactors was around 7-times higher than the open pond system. The RAB reactors also showed certain capabilities of removing metals from wastewater. The study demonstrated that RAB-based treatment process is an effective method to recover nutrients from municipal wastewater.